Xerographic apparatus



April 2, 1963 D. F. KELLER ETAL 3,083,622

XEROGRAPHIC APPARATUS Filed June' 12, 1959 2 Sheecs--Sheet 1 .Ezzanfars Daniel Frank/[h 'Kel/er.

M'l/l'am R. Bea/r, Jr:

United States Patent Ofifice 3,083,622 Patented Apr. 2, 1963 3,083,622 XERGGRAPHE APPARATUS Daniel Franklin Keller, Kenilwerth, and i 'villiam R. Beck,

.Ir., Ncrridge, Kih, assignors to Robertson Photo- Mechanix, ind, Chicago, Ill., a corporation of Illinois Fiied June 12, 1959, Scr. No. $19,351 1 Claim. ((31. 95-437) The present invention relates to improvements in xerographic methods and apparatus for producing printing plates or for reproducing copies in a substantially continuous operation.

Photographic xerography involves the formation of an electrostatic latent image on a layer of photo-conductive insulating material and the development of the image with a finely divided powder which adheres to the electrically charged areas of the plate. The plate is sensitized by applying an electrostatic charge to the surface of the photo-conductive coating. The sensitized plate is then exposed to the light image which it is desired to reproduce. Impin-gement of light on the photo-conductive coating causes electric charges to leak away or to be reduced in quantity in proportion to the amount of light falling on the particular area, thus leaving an electrostatic latent image. The image is developed by dusting the plate with a finely divided powder which adheres only to the electrically charged areas in proportion to the amount of charge remaining on the plate after exposure to light.

The photo-sensitive plate consists of a photo-conductive coating of vitreous selenium or the like on a backing of a material having a specific electrical resistance below the equivalent resistance of the photo-conductive layer. Thus, materials such as paper, glass, and plastics have been employed for backing materials.

The most common means for charging the photo-conductive layer to render it light sensitive consists in introducing the photo-conductive layer into an area of ions formed by corona discharge. The discharge is normally produced by applying a potential of several thousand volts on series of fine wires, so that the resulting electric field strength at the surface of the wires causes air molecules to be ionized.

The developing powder employed in one exemplary form may consist of two components, a finely ground pigmented resinous powder known as a toner, and a relatively large granular material having particle diameters of about A; to /z millimeter, known as a carrier. The carrier serves to add mass to the developer used on the exposed xerographic plate and also charges the powder particles to the correct polarity by a phenomenon known as triboelectrification. These electrical charges are generated by the intimate contact between the dissimilar materials when the developer components are simply mixed together. As a toner-laden carrier particle passes over an electrical discontinuity in the surface of the plate, the vertical component of the fringing field exerts a sufliciently large force on the toner particles to overcome the carrier-to-toner bond and the toner particles then attach themselves to the plate in the image area.

The present invention is directed primarily to an improved method and apparatus for Xerographic photography in which the sensitized xerographic plate is transported to an exposure zone, exposed, and developed as a continuous operation.

An object of the present invention is to provide an improved apparatus for the manufacture of xerographic exposures suitable for use as printing media.

Another object of the invention is to provide an apparatus for xerographic photography including a vacuum backed carrier which transports the Xerographic plate from a supply station through the charging, exposure, and developing stations in a continuous fashion.

A further object of the invention is to provide an improved method for xerographic photography on a continuous basis.

Other objects and features of the present invention will be apparent to those skilled in the art from the following description of the attached sheets of drawings which illustrate a preferred embodiment of the invention.

In the drawings:

FIGURE 1 is a view in elevation, and partly in crosssection, of a camera mechanism embodying the principles of the present invention;

FIGURE 2 is a view in perspective of the vacuumb-acked carrier employed in the apparatus of FIGURE 1;

FIGURE 3 is a fragmentary cross-sectional view taken substantially along the line IIIIII of FIGURE 1; and

FIGURE 4 is a wiring diagram for the circuits employed in the structure of FIGURE 1.

As shown in the drawings:

In FIGURE 1, reference numeral 10 indicates generally a light-tight chamber which includes the transporting mechanism, exposure mechanism and developing mechanism involved in the xerographic process.

A vertically movable platform 11 disposed within the chamber Ill carries a plurality of sheets 12 of xerographic plates, normally consisting of paper sheets having a coating of a suitable photo-conductive material such as vitreous selenium. The platform 11 is adjusted vertically by the provision of a pair of opposed pivot arms 15 and 13 secured to their respective shafts l4- and 16 and connected by means of a tie arm 17. A manually operable lever 18 secured to the shaft 14 permits vertical adjustment of the platform 11 as the individual sheets 12 are used in the process.

The mechanism employed for transporting the individual sheets 12 through the assembly is best illustrated in FIGURES 1 and 2 of the drawings. As best seen in FIGURE 2, the vacuum backed carrier, generally illustrated at numeral 19 in FIGURE 1, consists of a rectangular frame 21 carrying a plurality of rollers 22, the rollers 22 being arranged to ride on opposed tracks 23 extending horizontally along the walls defining the sides of the chamber 10.

A cover 24 is hinged to the frame 22 by means of a piano hinge 26 and is provided with a handle 27 to facilitate raising the cover 24 into the raised position illustrated in dashed lines in FIGURE 2. A vacuum manifold 28 is disposed at the rear of the cover 24 to apply a source of reduced pressure from a line 29 to a series of slots 31 formed in the face of the cover 24, as best seen in FIGURE 2.

The frame 21 is secured to a chain 32 driven by a sprocket 33 which, in turn, is driven by a reversible motor 34.

When a source of reduced pressure is applied to the vacuum manifold 28 through the conduit 29, the vacuum carrier 19 picks up a sheet 12 of the stock of sheets on the platform 11, and the movement of the carrier 19 takes the sheet, with its sensitized surface down, from a loading station indicated generally at A into a charging station or area shown at B, for example, into an ionized field produced by a corona discharge head 36. The latter includes a plurality of wires charged to a potential on the order of 4,000 to 10,000 volts, causing ionization of the air molecules in the immediate vicinity of the 'wires. As the sensitized sheet passes through the electrostatic field adjacent the corona discharge, the sheet receives a uniform electrostatic charge enabling it to receive an image from a suitable light source at an image receiving station shown generally at C.

After passing over the head 36, the carrier 19 transports the sheet to the image receiving station C which may include a photographic lens system of a camera generally indicated at numeral 37 of the drawings. The adjustable portions of the photographic system of the camera 37 may be preadjusted in connection with a vertically movable ground glass screen 38. The screen 38 is pro-positioned in the plane of the image member 12 whereupon an adjustable stop means may be preset to provide a positioning stop for the movable carriage 19 in the image station C. After the carrier 19 is positioned in the image receiving area C, it also strikes a contact arm 38 of a switch assembly 39 causing the carrier 19 to be stopped, by deenergization of the motor 34.

When the ground glass screen assembly is lowered into the position desired for centering the image and other adjustment, a switch 41 is deactivated by an arm 42 thereby deenergizing the motor 34. In the normal, retraeted position of the ground glass screen assembly, the arm 42 closes the switch 41 to make the conveyor system operative.

The operation of the switch 39 also serves to energize a timer 43 which is preset to determine the exposure time for the photographic system. Any suitable aerial image is projected by the camera 37 onto the image member 12. At the conclusion of the required exposure interval, the timer reenergizes the motor 34 so that the now exposed xerographic plate bearing a latent electrostatic image is passed to a developing station indicated generally at D where the latent electrostatic image produced during the photographic exposure is developed, for example, with a mixture of toner powder and carrier particles.

The applicator or developing station D may include a trough 44 containing a supply of the powdered xerographic developer mixture, and a rotary magnetic brush assembly 46 arranged to pick up the developer particles and apply them to the surface of the exposed xerogra-phic plate. The brush assembly 46 is rotated in a counterclockwise direction as viewed in FIGURE 1. A substantially uniform deposit of the developer particles is thus applied to the sheet and excess particles for the most part fall back into the trough 44. The brush assembly 46 is rotated by means of a motor 47 driving a chain 48 which in turn rotates a sprocket 49.

The exposed xerographic plate, with the developed image then moves past a safety switch 51 and eventually strikes an arm 52 of a limit switch assembly 53. The operation of the switch 53 deenergizes the motor 34 and stops the conveyor system.

The vacuum carrier plate 19 may then be removed from the conveyor assembly and opened to remove the exposed sheet from the face of the cover 24. The exposed sheet can then be fixed in any suitable manner, for example, a heat treatment which serves to set or solidify the resinous particles making up the exposed areas.

The cover '24 of the vacuum car-rier 19 is then lowered and a reversing button 54 is operated to reverse th direction of rotation of the motor 34, and transport the carrier back to the supply station A. Upon reaching the supply station, the vacuum carrier '19 contacts one of a pair of limit switches 55, 56 and thereby deenergizes the motor 34. The cycle is thus completed, and re-initiated by the operation of forward button 58. The sequence of operations, and the control circuits therefore, can best be described in conjunction with the schematic wiring diagram constituting FIGURE 4 of the drawings.

The entire assembly is energized by closing a line switch 61 connecting the assembly to a suitable source of voltage. Next, a switch 62 is closed to energize lights 63 which illuminate the copyboard on which the material to be photographed is located. Next, a switch 63 is closed to energize the magnetic brush rotating motor 47 and to energize a vacuum pump 64 to which the vacuum line 29 is connected.

To adjust the photographic system prior to making prints, the ground glass screen 38 is lowered to the image plane of the photographic system, thereby opening the switch 41, deenergizing the remainder of the circuit. A

three-position switch 66 is then moved to the focus position and thereby applies line voltage across a shutter mechanism 67 to open the shutter and permit focusing of the photographic system on the ground glass plate assembly 3 8. After this adjustment, the ground glass plate 38 is raised, thereby closing switch 41. Next, the switch 66 is moved to the on position. Since the vacuum backed carrier 19 is abutting the limit switch 55 at this time, line voltage is applied across a relay 67 having 3 sets of contacts, 67a, a holding contact, 671), a contact located in the timer clutch mechanism, and 670, a contact located in the energizing circuit for the corona device 36.

The vacuum applied to the manifold 28 by operation of the vacuum pump 64 conditions the plate to retain an image bearing member when platform 11 is elevated to lift a sheet 12 onto the face of the carrier 19. When this occurs, a pressure sensitive switch 68 in the vacuum line 29 is closed. Then, operation of the start button 58 serves to energize a relay 69, closing its three contacts 69a, a holding contact, 6%, a contact which serves to energize the corona device 36, and 690, a normally closed contact which opens the reversing circuit of the drive motor 34. The closing of contact 6% also serves to apply the line voltage across the drive motor 34 so that the conveyor mechanism is rendered operative in the forward position.

As the conveyor mechanism moves the vacuum carrier 19 away from the supply station, the limit switch 55 is opened, but energization of the relay 69 is maintained through the holding contact 69a.

The vacuum carrier i9, carrying the sheet 12 then enters the image receiving station, and eventually the carrier 19 closes the switch 38, thereby energizing a clutch 71 associated with the timer motor 43. Closing of the switch 38 also serves to energize a relay 72 having a pair of contacts 72a and 72b. The former is a normally closed contact in the energizing line for the corona discharge device 36, and opening of the contact 72a thereby deenergizes the corona discharge device. The second contact, 72b, serves to open the shutter 67 of the photographic mechanism.

At a predetermined time interval after the timer clutch 71 engages, rotation of the timer shaft serves to open two normally closed contacts 73 and 74. The opening of the contact 74 thereby serves to close the shutter 67. Opening of the contact 73 serves to deenergize the relay 67 thereby releasing the time-r clutch 7'1 and deenergizing relay 72. The closing of the contact 72a upon deenergization of the relay 72 thereby reapplies the line voltage across the drive motor 34 and renders the motor operative to resume operation of the conveyor mechanism.

The exposed xerographi-c plate then moves to a developing station where the brush 46, driven by motor 47 applies the mixture of toner particles and carrier particles to the exposed face of the xerographic plate. 7

As the vacuum carrier 19 moves toward the end of the conveyor system the carrier 19 engages the limit switch 52 thereby deenergizing the relay 69. Contact 6% thereupon opens, deenergizing the drive motor '34 and stopping the conveyor system. i

The carrier 19 is then opened to remove the exposed and developed xerographic plate. Upon movement of the cover 24 about hinge 26, the safety switch 51 is opened. After removal of the developed plate, and closing of the cover 24, switch 5 1 closes. Then, pressing the reversing switch 54 causes energization of a relay 76 having three contacts 76a, a holding contact, 76b, which energizes the reversing circuit for the motor 34 and 760 which opens to deenergize the magnetic brush driving motor 47 and the vacuum pump 64.

The vacuum carrier 19 thereupon returns to the supply station and at the limit of its travel strikes the switch 56 thereupon deenergizing the relay 76 and putting the entire system in readiness for another sequence of operation.

It will thus be seen that the apparatus of the present invention provides a complete and automatic assembly for providing xerographic exposures and developing on a continuous basis.

It will also be evident that various modifications can be made to the described embodiment without departing from the scope of the present invention.

We claim as our invention:

A xerographic machine for reproducing images directly on sheet-form copy media having a photoconductive coating thereon which comprises,

opposed tracks disposed horizontally and extending longitudinally,

a vacuum back sheet-form holder having a carriage supported for movement on said tracks, a platform subjacent one end of said tracks for carrying a supply of copy sheets,

said platform and said holder being relatively vertically adjustable whereby said holder may pick up and carry one copy sheet at a time from said platform,

a corona charging unit for forming an electrostatic charging field at a location adjacent said platform and through which the copy sheet is moved by said holder.

a motor drivingly connected to said carriage to move said carriage on said tracks,

pre-settable stop means for stopping said carriage and said motor at a stop position after said holder has moved the copy sheet through said charging field, a camera having a lens system for focusing an image to be reproduced onto a focal plane coincident with the plane of said copy sheet when said holder is at said stop position, thereby to fiorrn an electrostatic image on the photoconductive material,

and a xerographic brush extending transversely of said tracks having means for extending tufts of developer material in the form of a brush for contact with the copy sheet as the said holder is moved away from said stop position, thereby to develop the image.

References Cited in the file of this patent UNITED STATES PATENTS Ernst May 23, Simjian Mar. 27, Carlson Nov. 19, Carlson Oct. 6, OKane Mar. 10, Skinner May 4, Ransburg July 27, Carlson Sept. 28, Walkup Jan. 15, Gundlach Apr. 23, Whitham Dec. 1, Francis Nov. 29,

FOREIGN PATENTS Great Britain Feb. 9, 

